Bond behavior between surface-treated 3D-printed FRP bars and concrete

• Developed serrated 3D-printed FRP bars with 7.3 MPa bond strength. • Helically wrapped and sand-coated 3D-printed FRP bars had the highest bond strength. • Bond strength rises with concrete strength but drops with bar size and bond length. • The mBPE model effectively captures the bond-slip behavior of 3D-printed FRP bars. • Proposed bond strength model (R 2 = 0.93) incorporating surface roughness parameters. Although fiber-reinforced polymer (FRP) bars have been widely adopted as internal reinforcement for concrete structures, the conventional pultrusion fabrication process imposes limitations including reliance on molds and material waste. To address these issues, an innovative form of 3D-printed FRP (3DP-FRP) reinforcing bars based on additive manufacturing has recently been developed by the authors. In this study, a novel surface treatment for 3DP-FRP bars using serrated cross-section and sand coating is developed to enhance the bar-concrete interfacial bond performance. A total of 33 pull-out tests were performed to systematically investigate the effects of surface treatment methods, concrete strength, anchorage length, and bar diameter on the bond behavior of 3DP-FRP bars in concrete. Results show that untreated 3DP-FRP bars achieve a bond strength (the maximum average shear stress along the bonded length) of up to 7.3 MPa, markedly exceeding that of smooth pultruded bars. The bond strength increases with concrete strength but decreases with a greater anchorage length or bar diameter. The bars with a helical wrap and coarse sand coating (HWCS) exhibit the highest bond strength. Furthermore, the applicability of the modified BPE (mBPE) model for bond-slip characterization of 3DP-FRP bars is validated, and a new predictive equation for bond strength estimation is proposed.